There are two different kinds of hydroponic systems. One requires the use of a growing medium other than soil. The other uses air or water as the growing medium, leaving the roots exposed. Both types require a nutrient solution of water with dissolved minerals. Each type of system has three primary variations.
Hydroponic systems that require a growing medium generally use products such as sand, gravel and perlite, which is a volcanic material. Plant roots grow through the medium much as they would through soil. Nutrient solution passes through the medium to nourish the plants. Other types of medium that are commonly used are rock wool, coconut fiber and vermiculite. There are three variations of the medium type of system: the wick system, the ebb-and-flow system and the drip system.
The wick system is the most basic hydroponic system. A growing tray is filled with the medium. Within the tray are various wicks that deliver solution from a reservoir to the growing tray. Oxygen must be supplied to the water reservoir by means of an air pump. All systems that use a reservoir must also use an air pump, water pump or both to oxygenate the water.
The ebb-and-flow system is the second variation. The growing tray is filled with the medium. A water pump is used to supply solution to the medium from the reservoir. An overflow in the growing tray returns solution to the reservoir. The pump is generally on a timer.
The third variation is the drip system. The drip irrigation system supplies solution to the base of the plants. The growing tray is once again filled with medium, drip tubes are placed on top of the medium, and the solution drips down through the medium. A drain is placed at the base of the growing tray. The nutrient water is then returned to the reservoir or discarded, which is referred to as a non-recovery system.
Hydroponic systems that use air or water as the growing medium also have three variations: water culture, nutrient film and aeroponic. These systems have the advantage of no medium to replace or purchase. The disadvantage of two of these systems is that the roots are exposed to air. A power outage or pump interruption might allow the roots to become too dry.
The first of these hydroponic systems is called water culture. The reservoir is filled with solution, and an air pump provides oxygen to the solution. A floating grow tray is placed on the solution, and the roots are exposed in the solution. The grow tray can be constructed of any material that will float. Holes are placed in the floating tray, and small baskets support the plants.
The nutrient film system uses air as the growing medium. The growing tray in this system can be a large tube such as polyvinyl chloride (PVC) pipe. A water pump supplies nutrient solution from the reservoir, through the tube and back to the reservoir. Holes are cut into the top of the growing tube, and the plant roots are allowed to hang into the solution flowing through the tube. The growing medium is air, so an interruption of the water pump might allow the roots to dry out.
The aeroponic system is the final variation of the hydroponic systems. The growing medium is once again air, and the same disadvantage of pump interruption might damage the roots. The growing tray can be anything that can supports the plant above the reservoir so that the roots are hanging in air. The water pump supplies a fine mist of solution to the roots at specified time intervals. A short cycle timer is generally used with this system.